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' eoln ca[ echnus 2nc Page 3 Groundwater Monrtonng Report Project No 662 2 March 20,2001 1.3 Laboratory Analyses ' The groundwater samples collected on February 16, 2001 were delivered to Sherwood Labs (Department of Health Services Certification No 1400), of Hilmar, California, for analysis ' Sherwood analyzed the three monitoring well groundwater samples for • Benzene, Toluene, Ethyl Benzene, and Xylene (BTEX) by EPA method 602 • Total Petroleum Hydrocarbons as Gasoline (TPH-G) by EPA method 503018015(M) Additional samples were sent to Entech Analytical Labs (Department of Health Services ' Certification No 2346) from Sherwood Labs for the analysis of • MTBE, DIPE, ETBE, TAME and TBA by EPA method 8260 ' The detection limits for the above analyses are listed in Table 2 of Appendix A while the lab analytical results are presented in Appendix B ' 20 FINDINGS AND DISCUSSION The results of the groundwater sample analysts show the following • The laboratory results indicate MTBE continues to be present in wells MW-1 & MW-3 ' • MW-2, which is upgradient of the farmer U STs, remained free of detectable contamination for the fifth consecutive event • Neithei BTEX nor TPH-G was present in any of the groundwater samples above the laboratory reporting limits • Oxidation-Reduction Potential measurements (Table 3) show that the three wells at this site are not significantly impacted by biodegradation of a BTEX/TPH-G plume The values have decreased by an order of magnitude, but are still positive, suggesting that there is a limited amount of biodegradation of the contaminant plume occurring This is to be expected, since the primary contaminant is MTBE, which is very resistant to biodegradation The lateral extent of the contamination is only defined upgradient to the northwest by MW- 2 The vertical extent has not been defined GTI makes the following recommendations • Perform additional soil and groundwater investigation by installing borings and monitoring wells to define the lateral and vertical extent of the plume and to evaluate the mass of contaminants present In our January 15, 2001 work plan, GTI proposed the installation of seven direct push probes to achieve additional plume definition The